Okay the reason I asked was to rule out the exclusion of gain for primary residence.
Publication 523 is also another resource that has some more details about improvements that count.
As for adding up your costs. There is a rule noted as the Cohen Rule from tax court cases that allows for reasonable estimates to be used for costs in the case records can’t be found/provided
. In general the IRS would/could be satisfied by a reasonable estimate of the cost at the time period, and there is some sort of general evidence that the improvement exists (ie you can see it) that should help with coming up with your adjusted basis add ons. For instance if earth moving work costs $xxxx now, it would be reasonable to assume it was $xxx years ago. Does it align with inflation, your memory, etc. Making common sense goes a long way here. Any and all materials you can find, drawings, permits, etc. help build a strong case.
Hope this is helpful! Let me know if you have further questions.
