One Penny Stamp - Details Resembling Plate Number.

This, certainly, is not one of those 'plate repair' stamps as they were the imperforate versions of the 'Penny Stars.'
GeoffHa's explanation may be valid. It may be the case that wear and inking have caused a shape resembling a '2.' It looks like a script '2.' The plate numbers tend to be very basic numerals.

Here are the 2s in plate 224.

I agree with Bobby De La Rue.
I don't know how this occurrence appeared there . Of course it could be random or it's some type variety ,l can't be certain.

Of course l can't say whether this is kase of wear of the plate on this particular area ,which could have caused this difference. The posting of the image of the imperforate issue is only to compare the two details. Of course it's not from 'plate repair'stamps but it's interesting to point tath if you look closer you could see tath the two details are placed on the same position of the stamp, the shape is also very similar . The other question which puzzles me, if this was caused by some random reason like inking why this detail appeared on the same position on the stamp published at "Great Britain line engravet plate repais 1840 to1855" ?

These stamps have an engine-turned background. The details are not always clear. Sometimes, they do show. If you look to the left of the spot you mark in the link, or to the right (partly obscured by the cancellation), or to the northeast, you will see the same type of spots. These spots occur in many places on these stamps. If billions are printed, you will find them in similar places on stamps from different plates.

Look just above the first '2' in the plate number I posted. There is a similar spot there.

Many such spots on a Penny Black from plate 3:

Of course, l fully agree with you
that majority of the penny stamps have many little differences in the design caused during the printing process like overinking which some times makes the plate numbers to appear in many unusual forms or even resembling letters .
It's not uncommon to confuse one plate number with other. Yes there are small dots or spots on the margins ,l observed them before there are visible always at this area of the stamp.

Yes, l can see these spots very clearly, from the image you've posted but l can't see a number on either sides. Yes it's very logical to presume that a random plate error or some other problem occurred when the stamp was made could have caused this detail to look like the number "2" . I examined lots of images of stamps from the same issue but couldn't see a similar defect.
I understand that there are many other stamps which might have the same occurrence but the only identical to it stamp l could find with the same detail is the imperforated penny stamp from "Great Britain line engravet plate repais 1840 to1855".

There are just four plates from which imperforate - other than imprimaturs - and perforated stamps are known. Comparing the ones in your book to your stamp that is likely to have corner letters from a different alphabet is a ghost hunt.

Your spot is in exactly the same space as one in my Penny Black. It is part of the engine-turned pattern. The shape is slightly different, which has to do with plate differences, inking, and wear.

Also consider how often you use "Yes / I agree ... but ...."