i think what you’ve described here is unfortunately the easiest way to do this, although it’s not super precise in terms of fulfilling exactly what you’re looking for. if you want more precision, you would need to use the API’s identification endpoint.
pull all the results for your identifications (ex. loop through all pages of https://api.inaturalist.org/v1/identifications?taxon_id=469282&user_id=dan_johnson&per_page=200), then pull all the results for the other person’s identifications (ex. loop through all pages of https://api.inaturalist.org/v1/identifications?taxon_id=469282&user_id=billreynolds&per_page=200), and then exclude results in your set that have a matching observation id in the other set (which can be done via, say, a SQL query or VLOOKUP in Excel or Array.find(key) in Javascript.
once you have a list of obs IDs that you want to lookup, you can just share the list of obs IDs, perhaps making sure that you can click on an obs ID to navigate directly to the observation’s URL. alternatively, you could group the obs IDs in chunks (maybe around 300 obs IDs each) and create several links to the identify screen that pull back specific observations. for example:
https://www.inaturalist.org/observations/identify?reviewed=any&quality_grade=needs_id%2Cresearch%2Ccasual&id=54259799,54261030,54264838,54258480,54259085,54256138,54235902,54237224,54242140,54230631,54220535,54213509,54214228,29465163,27599315,51629723,54208586,54196490,54203068,54205074,54174973,54176555,54178879,54154908,54153917,54127259,54127400,54101524,54102578,54103366,54103451,54093044,54080213,54092468,54069316,54048580,54055934,54045235,54038876,54023835,54026005,53991846,54013423,54017903,54019116,53976698,53981519,53966622,53968211,53970501,53973192,53974740,53955251,53941686,53941830,53918422,53938968,53940166,53909557,53897744,53894854,53895924,53892347,53892421,53855476,53861791,53882924,53839107,53839584,53848933,53850500,53854450,53830610,28907290,53806468,53810284,53810705,53791570,53759488,53763350,53770169,53772582,53781963,3828485,38126134,49760999,51374302,52409646,32283376,32449111,33489049,33682097,34495630,31572733,31671932,31950945,32054403,31016164,31061126,31087941,31322787,31327125,30635605,30711098,30742326,30937436,30008653,30252416,27806292,28732157,29380668,29593595,29820224,15973939,16019299,16099597,16168937,14838639,15019252,15131959,15286091,15393852,7859979,7861147,7862139,7935879,4013410,4020614,4841237,7419174,7421092,7575604,3771368,3776743,3786221,3812803,53752663,53754212,53754805,53736915,16958763,53720943,53728378,53731941,15207377,15411052,15690519,15917691,15988742,16300047,16308399,16331542,28557131,30139696,3695906,3852129,3940883,3964083,4979095,7580090,7625201,8167252,8167840,8380795,15151659,15154375,118893,1897717,1907345,31169794,31602954,31827499,32644116,33173161,33962276,35399260,39638130,39907778,4950525,7639013,7964228,8036906,14366323,53694229,53710251,53716993,53720242,53722127,53669000,53673169,53673231,53674030,53684576,53642230,53635360,53600014,53615293,53615700,53615933,53624712,53586488,53590897,53597491,53597737,53559304,53566593,53559349,53563785,53564975,53576336,53541906,53553238,53530159,53532310,53506026,53506701,53514087,53515990,53516544,53489489,53499643,53478877,53481466,53470737,15321928,15224688,31880995,31686955,53460161,15424436,13600217,44364,338865,53425143,53428522,53418416,34171942,33432758,33433094,33441947,33573404,31509422,32393393,7796109,15261002,15261003,2937389,6820766,7494912,7616796,32318186,15120503,774507,3843951,16636959,17094648,31011768,34166446,34176062,39427591,373904,7622538,15985451,33288453,36194665,51900997,53260180,53260635,32169693,32239547,32239548,32659344,32715414,32783350,31433270,31496434,31721625,31789167,32001649,31015289,31052496,31090604,31118323,31318198,29519434,30252681,30490948,30502966,30933623,30936170,30964562,31004598,31004737,31007782,17759165,17780980,18439136,26551042,28285881,28627425
another possibly easier way to do the above is just to get your IDs (ex. loop through all pages of https://api.inaturalist.org/v1/identifications?taxon_id=469282&user_id=dan_johnson&per_page=200), translate that into a list of observation IDs, group those observations IDs in chunks (of, say, 300), and then create several links to the observation IDs, relying on the reviewed flag to filter out the observations that another identifier has already reviewed. for example:
https://www.inaturalist.org/observations/identify?quality_grade=needs_id%2Cresearch%2Ccasual&id=54259799,54261030,54264838,54258480,54259085,54256138,54235902,54237224,54242140,54230631,54220535,54213509,54214228,29465163,27599315,51629723,54208586,54196490,54203068,54205074,54174973,54176555,54178879,54154908,54153917,54127259,54127400,54101524,54102578,54103366,54103451,54093044,54080213,54092468,54069316,54048580,54055934,54045235,54038876,54023835,54026005,53991846,54013423,54017903,54019116,53976698,53981519,53966622,53968211,53970501,53973192,53974740,53955251,53941686,53941830,53918422,53938968,53940166,53909557,53897744,53894854,53895924,53892347,53892421,53855476,53861791,53882924,53839107,53839584,53848933,53850500,53854450,53830610,28907290,53806468,53810284,53810705,53791570,53759488,53763350,53770169,53772582,53781963,3828485,38126134,49760999,51374302,52409646,32283376,32449111,33489049,33682097,34495630,31572733,31671932,31950945,32054403,31016164,31061126,31087941,31322787,31327125,30635605,30711098,30742326,30937436,30008653,30252416,27806292,28732157,29380668,29593595,29820224,15973939,16019299,16099597,16168937,14838639,15019252,15131959,15286091,15393852,7859979,7861147,7862139,7935879,4013410,4020614,4841237,7419174,7421092,7575604,3771368,3776743,3786221,3812803,53752663,53754212,53754805,53736915,16958763,53720943,53728378,53731941,15207377,15411052,15690519,15917691,15988742,16300047,16308399,16331542,28557131,30139696,3695906,3852129,3940883,3964083,4979095,7580090,7625201,8167252,8167840,8380795,15151659,15154375,118893,1897717,1907345,31169794,31602954,31827499,32644116,33173161,33962276,35399260,39638130,39907778,4950525,7639013,7964228,8036906,14366323,53694229,53710251,53716993,53720242,53722127,53669000,53673169,53673231,53674030,53684576,53642230,53635360,53600014,53615293,53615700,53615933,53624712,53586488,53590897,53597491,53597737,53559304,53566593,53559349,53563785,53564975,53576336,53541906,53553238,53530159,53532310,53506026,53506701,53514087,53515990,53516544,53489489,53499643,53478877,53481466,53470737,15321928,15224688,31880995,31686955,53460161,15424436,13600217,44364,338865,53425143,53428522,53418416,34171942,33432758,33433094,33441947,33573404,31509422,32393393,7796109,15261002,15261003,2937389,6820766,7494912,7616796,32318186,15120503,774507,3843951,16636959,17094648,31011768,34166446,34176062,39427591,373904,7622538,15985451,33288453,36194665,51900997,53260180,53260635,32169693,32239547,32239548,32659344,32715414,32783350,31433270,31496434,31721625,31789167,32001649,31015289,31052496,31090604,31118323,31318198,29519434,30252681,30490948,30502966,30933623,30936170,30964562,31004598,31004737,31007782,17759165,17780980,18439136,26551042,28285881,28627425
here’s a wrapper page for the API endpoint that may or may not help you to view and use the API a little more easily: https://jumear.github.io/stirfry/iNatAPIv1_identifications.html?taxon_id=469282&user_id=dan_johnson&per_page=200.