??? There are only ten digits, and you don't even need all of them everywhere. By my reckoning, you would need 3+10+6+10+6+10=45.
If you add the ability to display dd-mm-yy, you till would only need 3+10+6+10+10+10=49. I wonder what they did with the remainder. Spelling out the word "ALARM!"?
Or did they simply ship spare bulbs inside the product?
That still leaves the question of why 12 lights instead of 10. I would bet that the separator colons are actually produced by a separate mask+lamp, rather than having different masks for each digit on those two modules. I.e. to show "8:" you light up both the "8" lamp and the ":" lamp at the same time. That gets us up to 11. No theory on the 12th one though.
(I still write it like that, in handwriting.)
The detail for what the extra masks were for is unclear, but it does look like there were 12 per digit.