Bf 109G coded with additional letters

Gentlemen,
I always wondered (but never "dared" to ask about ), what are the small letters added to some of the numbers of ARR Bf 109?
I know 2 popular photos of a/cs coded in this manner. The first one is from the book “Romanian Aeronautics in the Second World War":

And the second one is from a source I don't remember any more, but it can be seen in the collection of photos @ the Falcon's Messerschmitt Bf 109 Hangar site here:

As per the description from the above site, the additional letters were used on the second (or third etc.) a/c coded with the same number. If so, on the second photo this must be the third a/c coded 23 in one and the same unit.
Is this the correct explanation? Is it known when these “extended” numbers were in use?
Thanks in advance!

The description on the site is correct. The suffix letter ( a, b , c) added to the number denote the change of the lost plane with a new one in the same unit.
The "extended" numbers for Bf 109G were in use starting with summer '43 with Grupul 7Vt and later with "Grupul 9Vt" on russian front until spring 44. In summer 44 there were no evidence of the use of such identification ( probably due to the many Bf-109 received in both units and few pilots available to fly them)

Thank you very much - your answer is highly appreciated!

Same was with the Ju 88's

And HS129s

Yep! Now when you mention it, I see I didn't check my references very well (e.g. Denes' book, page 57/58 or "Romanian Aeronautics" page 196).
Thanks again!