the county records are reliable. the deed office can tell you when the deed transferred and from that when comparing to the date of death you can determine if the quitclaim occurred prior to the death of whomever your MIL may have inherited it from. The county may have record of what the property originally sold for,
if it goes back 60 years, I can't imagine there is much of a difference between what it was worth at quitclaim and or inheritance...and remember the impact is really only 15% of the value, because it's the capital gain tax that is the end issue.
