Last year, I got 3 LNF for non-refundable rates approved 1month after the reservation was made, using a third party website=) They were all approved in one-go=)

while I have no reason to disbelieve you and because of the 24-hr rule have never filed an LNF claim beyond this time (frankly would never even think of doing so), per the T&Cs of LNFs:

How much time is needed to process my claim?
Marriott Customer Care will process all claims within 24 hours of receipt. However, please keep in mind that the comparison rate must be found, and a claim submitted, within 24 hours of your initial reservation. In addition, to assure we can process your claim in time for your arrival, claims must be submitted at least 24 hours prior to hotel check-in.
https://www.marriott.com/hotel-prices/faqs.mi

Either you are really lucky that they overlooked the rules or the LNF dept is totally incompetent.

Anyway, there is another thing OP could try: call the hotel directly and ask if the hotel could match the rate for the whole period of time to EUR 198 per night. It's up to the hotel to decide but I did hear an IC agreed to match the rate or give you some credit to spend at the hotel.