WR802N different maximum transmit power depending on batch?

I have an about 1 year old WR802Nv4 and 2 WR802Nv4. All three are set to Australia countrycode.
Old WR802N has 25 dBm transmit power.

Both new WR802nV4 have only 22 dBm transmit power. That is only half of the power of the other device.

In both cases it is MediaTek MT76x8 802.11bgn chipset. So how can this be?

EDIT: Corrected. All are v4 devices.

I've also measured the signal strength of older WR802Nv4 and current one. There is really about 3 dBm weaker signal with the newer AP.

When copying /dev/mtd6 from older WR802Nv4 with 25 dBm maximum transmit power, maximum transmit power is only 21 dBm, instead of 22 dBm. Can somebody explain whats going on here?

Different hardware may provide different specifications, news at 11.

You either have to ask TP-Link for the details (which they aren't going to answer) or study the FCC tests and take a microscope to the PCB, to reverse engineer the rf path and the components used therein.

You might want to clarify how many of which version you have, v3 and / or v4.

All are v4. I have no v3. Only difference is one v4 bought about one year ago, and the other two bought the last days. That is why I am so confused.
Edited the first post, it was typo. All are v4 devices.

I've ordered new WR802N from other seller and these have 25 dBm maximum transmit power.
So:
SN beginning with 219 and 220 maximum transmit power 25 dBm
SN beginning with 221 only 22 dBm maximum transmit power (ordered from Amazon).

But also: Both 219 serial number and 220 batches are from "TP-Link Italia", whereas 221 batch is from TP-Link Germany. So maximum transmit power might not be dependent on serial number, but by production department.

If maximum transmit power is dependant on serial number: From my experience Amazon has quite a small stock so you usally get the latest version of products. In this case this is not optimal. Try to get if from a medium sized seller. Thats where I got the batches with SN220 and 25 dBm transmit power.