搞不懂你的问题.

if you've never reported, the "carry over" is not valid.

If you know and reported so that you can "carry over", you won't ask this question.

Puzzled.

So suppose you've reported, and still have loss after years' of rental income, it is included in combination with the report of your new investment.

NO, it is not called deduction by all means. Actually it doesn't matter, just combine all the gain and loss and see what is the end results.

If you already had all tax returns messed up for past few years, start straighting them from the first year of having rental income.