Alas, the number on the picture frame and elsewhere are the
car number (e.g. 1Rnnnn).
The
body number would be something like 4Rnnnn and was recorded on the data plate and also a tag riveted to the rear panel to the right of the license plate. The OP replacement of rear panels apparently removed that.
The body number on mine was also written (just the last 4 digits) in a couple of places using yellow crayon. But those marks were not consistent and often go missing through the years.
A build certificate will show all numbers but usually they will only issue one using the numbers you provide - numbers you do not provide or are wrong will be left blank. This is to keep someone from obtaining a picture frame and building a car to go with it.
Here is the form for a research request, they also do the heritage Certificate:
https://www.jag-lovers.org/jdhtform.htm?nuc=1
The dollar amounts on that form may be out of date so an email is best initial contact.
It is just possible an email to Gloria or Mike explaining your situation might get you dispensation for the missing number.
Mike's email (last time I corresponded with him) is: mcook69
at jaguarlandrover
dot com
The tag you see on the pillar is also the car number, apparently
1R9940.