That someone would swap a BKP backplate onto another pickup is extremely unlikely - that would involve dismantling a genuine BKP, which would be pointless, for no apparent gain.
Two factors are at play here.
Firstly, your expectations - while the voice of the Miracle Man is not dissimilar to a scooped EMG, they will still feel very different. High output for BKP is still not going to be as high output or compressed as an EMG, as EMGs are in effect a weak pickup with a strong pre-amp attached.
Secondly, it sounds like you don't have a set of Miracle Man (Miracle Men?). BKP don't label their pickups, so unless you buy them new, you have no certain way of knowing what pickup you've got. Someone could have been mistaken previously or mis-sold them and passed that information to you, but what you're describing doesn't sound like the MMs. It also means you have no way of proving to the seller you got them from that they're *not* Miracle Men, so you're probably best selling them on as unknown BKPs with as much information as you can gather.
If you have a multimeter, take readings of the DC resistance and see if they're close to any of the stated figures on the website, as that might help narrow it down. Similarly, if you can take pictures and send them to the BKP team, sometimes the height or thickness of the coil can be the clue they need to identify them for you.
