skwkevin,
Interesting question. The website https://www.thetaxadviser.com/issues/2015/jul/hollingsworth-jul15.html while somewhat old, seems to be quite authoritative and quotes from Regs. Sec. 1.871-7(c)(3):
"Capital loss carryovers and the small business stock exception under Sec. 1202 are not taken into account in determining a taxpayer's net gain"
for nonresident aliens. As this directly implies that nonresident aliens can have capital loss carryovers, albeit generally unusable on their 1040-NR tax return, my read is that the carryover must clearly continue to exist into the year when he or she becomes a resident alien.
How to handle it without prior year Schedule D's would need to be handled by both claiming the carryover on your Schedule D and appending a statement to your return explaining your position. Even if the IRS disputes the carryover, all they will do is send you a letter asking for more tax and a bit of interest for the extra up to $3,000 of income declared but not taxed. No, they won't try to put you in jail.
