Is This Overprint Genuine Or Fake?

It does coincide with the Chudleigh 1844-type inverted cancellation that was in use when the stamp was current. Folkestone may be less likely. You could be right it is the inverted '202' numeral.

Your guess as to why someone did this is as good as mine.
Collectors do strange things to fill gaps, Forgers do many things to mislead people.

For example, a faker/forger might practice on no/low value stamps to check out the rubber stamp, ink, or strike force.
Don

If you're going to make a high-value fake, you might as well salt it in with some low-value fakes so that the overprints match. That might fool the low- to no-effort viewer.

Thank you gentlemen, yes, a practice run is obviously on the cards on a low-cost item with overprint and cancellation...

A test run, however, would indicate a consequent campaign of subsequent higher-return forgeries with, I presume, a certain number of 202 cancellations.

Sorry if I bore you with my reflexions.

I wonder if Chudleigh even had an Inland Revenue office. It is quite a small town.

KLJ30000,
We all can speculate on possible faker's intentions for weeks, in my opinion the most obvious explanation is that it is a fake overprint.

If anyone thinks it is genuine, then the obvious task is to prove it. This would be done by finding documentation, other postmarks, other covers, or other stamps that support that belief. Without this; Occam's razor.
Don

Plate 11 was put to press on 25 January 1872. The plate was used to print the 6d in chestnut on paper with the 'Spray of Rose' watermark.
Plate 12 was put to press on 30 October 1872. Stamps from this plate were printed in buff on paper with that same watermark. On 24 April 1873, the colour was changed to a distinct grey. Plates 13 through 17 were also used with grey ink.

There exist stamps from plate 13 in the buff colour. These came from a printing from which the imprimatur sheets of the plate were taken. The extra sheets were perforated.

On 1 January 1881, the stamp printed in grey from plate 17 (first put to press on 21 April 1880) on paper with the 'Imperial Crown' watermark were put to market.

From, at least, late 1873, no stamps have been printed in the chestnut or buff colours.

Overprinted 'OFFICIAL' stamps were not considered before well into 1882 and printed from plate 18 (first put to press 18 January 1881) that only was used for printings in grey on paper with the 'Imperial Crown' watermark.

Anyone trying to prove - and I doubt anyone is - this could be an official trial or even an official issue will have an enormous task to explain the 9 to 10 years' gap between the phasing out of the chestnut / buff ink and the consideration of any 'OFFICIAL' overprint. Also, the watermark was changed more than a year before these overprints were suggested,

thank you, gentlemen, it's almost comic, is it not? However, it is still part of a process; I will put it to bed for now and will let you know if I find anything.

Is there a thread on QV Abnormals?

Not that I am aware of. I have not encountered any posts on them.