Help With Potential Czech J52A

I acquired this stamp in a Centennial Stamp auction. It sure looks like it could be a J52a worth >$50,000. Would appreciate assistance.

Hi J.A.,
What an intriguing find! One's heart always pauses for a sleeper. Hopefully yours is.
The issue on this stamp is whether the overprint is genuine.
I have been studying the 1919 overprint series, which is different, of course, but counterfeits are rife. The default hypothesis with a stamp this rare is, this stamp has a fake overprint. So if I found your stamp, here's how I would approach it.
1, Are there any marks on the back, like an expertization mark?
2. I'd get a little collection of comparisons - the 50h overprint appears on the 20h and 150h values in this series. Get a bunch of those. You can also form a pdf collection of the 50h on 50h genuines (I guess there's less than 20 known) from auctions (like Flaska or Burda's on-line archives). You can also harvest pdf's from ebay sales of the common 50h on 20h and on 150h.
3. Closely compare every detail and proportion of the overprint's letters size, shape, and spacing that you can between the subject your "find" and the samples in your little collection.
4, It really helps to take scans and blow them up a bunch on your computer screen. An 8" stamp is easier to analyze than a bitty 25 mm high one. You can measure things with a ruler in 1/4 - 1/2 mm on your screen pretty easily. Or blow them up to the same scale, using the printed stamp boundary as a size guide, and then compare with a light table or meticulous viewing.
5. Also, there's a technique for taking a cheap genuine overprint, carefully slitting narrow holes along the overprint, and laying it over the subject to see if the overprint letters exactly line up in size & shape.
6. You're looking for discrepancies.
7. Or, send it to Marek Vrba in Prague, Czechia. He's the expert to ask. I'd do this after I assured myself the overprint on your subject stamp exactly matched that of your samples of 50h on 20h's.
8. Also, there may be literature on what cancellations are known or expected, and see if yours falls reasonably within that range.
(It looks to me on short review that the "5" is fake because when I do a split screen between the subject and a known reference, the bottom of the vertical stroke of the 5 has a square peg on your stamp and the reference has a rounded knob; there seem to be inconsistencies in the shapes of the letters between the subject and the reference as well - but this is just a quick look on my part.)
Good luck and let us know how it turns out!

IMO it is a fabrication. The perfs of your stamp are all wrong for this issue and the underlying numerals are conveniently covered by the cancel.

More here:

https://stampauctionnetwork.com/iCa...SrchSale=359

I think the perfs of the subject are fine. They look like comb perf at 14, just like the 50h on 50h; the auction exemplar that rogdcam listed is a very clean example, but both the subject and the exemplar are comb 14's. The subject has a very old worn out comb perforator; it is common to find a popular issue like the 50h allegory to have some examples with crisp perfs from fresh perforators and worn doggy looking perfs from old combs.

Anyone trying to fake the 50h on 50h would start with genuine cheap-o 50h's and add their own fake overprint, No point in re-inventing the wheel to get the base stamp right. You just need the fake overprint to make a bigger sale, right?

This stamp has been clearly altered. Look at the left non-overprint denomination and notice the purplish discoloration next to the 5 of 50. That is where the 1 of 150 should be. You can also see some of that purplish color where the right 1 of 150 would be. The cancel is strategically placed to help with the deception. Look at a genuine J 52a below and pay careful attention to where the 50 denomination lands in relation to the design edge.

Not only what @rogdcam said, but the zeros don't have the red lines in them.

It does look like rogdcam called it. The size and shading of the numerals suggest the underlying stamp in the OP was a 150h stamp.

I think we must be missing something as I went through my collection and found the following:




As NicholasC said, it looks like a different base stamp as there are no red fillers in the base stamp numbers.

It could be a forged base stamp AND forged overprint.

Now that I magnified it, mine is a 150