If something is marked "Patent Pending" you can reasonably assume it was made within a year or two of the patent being issued.
2014 was the last year for the two letter code system. = 2015** *: Used in conjunction with date codes AT and AH respectively. There are examples of 1981 “C” code Weber’s that have been seen with a small “D” stamped near or on the opposite side of the “C” stamp.
These examples are believed to be the actual 1982 kettles and WSMs.
NOTE: It is advised that any drawing/s necessary to understand the subject invention should be submitted at the time of filing so that there would not be a possible change in filing date due to late submission/filing of said drawing/s .
(Rule 602 of the IRR)The other formal requirements, which are not needed to obtain a filing date, but maybe included at the time of filing are: (a) A filing fee (for big or small entities) which maybe paid during application filing or within one month from the date of filing. Formality Examination Upon receipt of the application, the examiner checks if the application satisfies the formal requirements needed for the grant of a filing date.
If you have ever had trouble dating old instruments, this list may be a help.