Aquatimer 1816? identification

Hi there, I recently got an old IWC Aquatimer in very used condition. End of last year I decided to send the watch to IWC for a complete restoration. I got the watch back and IWC did a fantastic job bringing the watch back to life. See picture. Unfortunately IWC did not give my any detailed information on the watch history although I spend a fortune for restoration.
Anyway I'm still uncertain regarding the watch reference. According IWC it is a Ref 1816, but the watchcase and the dial(812?) is not like a 816 should look like. Can anybody help me to understand the correct reference?
Details:
Serial movement: 2001751
Movememt: 8541B
Case back: Submarine,no ref number mentioned,serial 2014388, BREVET+487449

I would appreciate any comments helping identification. Thanks

Pictures after restoration

Really difficult to know the exact ref. of these aquatimer. In my opinion the 1816 have the external bezel with 14 sides, while the 1822 must have the external bezel completely round, but I am sure that there are some 1816 with the external bezel round......Further your aquatimer seems with the external bezel round ( like a 1822 ) but the dial is completely unknown ( at least by me) It seems a little bit as a 812 but it is not ( never seen a 812 with a triangular dot at 12 ) At last the two 1822 I have seen were without the submarine on the back while yours come with it.....May be during the '70 many oddities were allowed on these watches. Suggestions, comments experiences should be much appreciate.

IT would be great to see more pictures from strait on of the dial, and of the case back- that would help.
You seem to have an interesting one here, for sure.

Nelson

Thanks for friendly reply. Here some more pics.

HI,
I believe you have an odd mix- indeed, the outer rotating bezel is from the 816, as is the case. However, the inner dial is from a 812 AT, and I believe so is the round bezel. As Giuliano said above, maybe there were some mixes during the 70's, but IMO this watch is a mix of parts from the 812 and the 816.
Was that the original way it looked when you sent it to IWC for servicing?
Nelson

Thanks for comments. The watch was heavily used over the years and had serious signs of use and was not working. I sent the watch to IWC for service and repair and IWC sent me the watch back in 'as new' condition. The dial and outer ring were not changed and not refreshed, only the pointers have been replaced (but same style as before restoreration).

None the less, a great looking vintage piece! Enjoy it.

Nelson

IWC did a good job. The watch is beautiful!