House deeded to son in 1998.  Cost 40K, FMV 800K. (Gift tax unknown)

House sold in 2022 for 750K.  The 2-year use requirement not met.

1/2 of the sale price was received in 2022 and reported on 1099-S.  Per a legal agreement (made several years before the sale), 1/2 of the sale price will be received in a future year upon the passing of the owner-mother of son.

This could be an installment sale.  There could be a world of tax when the other 1/2 is received.

I suppose I need the legal agreement before I make a final tax determination. But as of now, the future is the future.