Yes, you can have your experience reviews “as you go” if you so desire. It’s less efficient than doing it all at once, but at least you’ll know that your experience to-date is accepted. You can’t have your experience “pre-approved” though, so if you don’t finish until next year they’re not going to approve that portion until next year. You’ll still have to submit the final 12 months along with the new L3 passers. You will have the benefit of any CFAI feedback on your prior submission though, so you should have no problems getting the last year approved. A lot of folks word their submission “poorly” and end up having to resubmit it a few times before it gets approved.
I would also advise you to join your local society in the spring as a candidate so you don’t have to wait for them to accept you when all the new passers are trying to join. I think if you join late enough in their fiscal year (June 30th), they waive the fee.