What year was my MkIIIB Ross built?

I have a 1910 Ross MkIIIB - one of the British contract rifles with the unusual rear sight.
The serial number is H8**. I came upon an internet search where someone said all these rifles had a letter followed by a number. What number did they switch to the next letter? If anyone knows the pattern it would tell me what # this rifle was. A sequence going to 9999 would be too much as this would then be the 69,000+ rifle made and that does not seem possible. I understand only 66,591 odd versions were built before the UK cancelled the contract.
I suspect these were some of the last Ross 1910s to be built. 1916??
If any of you Ross guru's could help me establish WHEN this rifle was built it would help me complete the history on it.
Thanks!

According to "The Ross Rifle Story", the serial number was stamped on the left side of the receiver and was composed of a Letter and Numerals.

Rifle E9335 is shown on page 180 of the book.
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