C-Type Head on a 1956 XK-140 OTS

Perplexed and hoping someone can shed some light on the subject. I am in the 4th month of a restoration on my XK-140. I just received my heritage certificate and next to the chassis ledger it is noted "less C-Type head. This must be true as a physical inspection has revealed that the cylinder head is not colored red nor has the letter "C" been cast in the Valley. A little light reading on the subject has led me to Philip Porter's 2nd Edition Original XK Restoration guide and his discussion of the Special Equipment Models. According to Mr. Porter, the C-Type head was standard issue on all Home Market SE models, but was an option on exported models of the SE. My car was exported and sold to its original owner in Ohio. Mr Porter goes on to say that "but in practice this was not so - a large number of SE 140's had the words"less C-Type Head" added by their entries in the Chassis ledgers." He goes on to say "the prefix A to the chassis number denoted an SE 140 (190bhp) and the prefix S an SE fitted with C-Type head (210 bhp). The question is that if I do not have a C-Type head then why do I have a chassis # starting with an S prefix and even more perplexing is why does my engine have C-Type Version Cam Covers which have been physically verified. Why not standard cam covers for a standard cylinder head. Something doesn't add up. This is a numbers matching vehicle, could this just be an enigma attributed to some sort of transition in evolution of the XK engine? Hoping for a little insight. Thanks.

Jaguar 3.4L XK 140 Special Equipment Model OTS LHD Chassis # S812197