Hmmm............. The 3 sources I have for Mariner seem to disagree- 2 put that serial number at 1983, 1 puts it at 1982. Regardless, none of them show the outboard as 1987.
On numerous occasions over the last few years of looking up many serial numbers for forum members here and on M.E, I've personally found the serial number charts to be more as a general guide then to be 100% accurate.
When I had access to the Mercury dealer website, I used to run the numbers that would say the year and also provided the model number confirming the year and in some cases when comparing the charts, they seemed to be off by a year or three....It was more the serial numbers that started with 695, etc. etc.
Not all serial numbers are available though.. For the ones that are, the computer system seems to be accurate from 1980 on up. I've seen a few 1977's -79 though but not many.
So personally before going to the charts now, using a few websites, I run the number and look for a model number which some members are looking for as well.
There's a small trick to looking up these type of numbers though.