You may disagree with what I am about to write, but hear me out:
You are interested in a mic that, if my research is correct, will cost around $20,000.-
You are rightfully concerned whether this would be a good investment for you, considering that that kind of price should guarantee a high level of authenticity, of 100% period-correct parts throughout, of no alterations, etc.
But now comes the split in the road: because you somehow think expert advice can be obtained without engaging a third, unbiased party, which needs to get pay for that advice, you post in on-line forums, hoping to get that advice for free.
Looking at any other field of high-priced collectibles, you would instantly recognize the folly of this. Just imagine, you were to post on an internet art forum: "I am about to buy this Picasso, but I see some funny brush strokes in the left lower corner. Is this a real Picasso?"
When we engage a professional service, there is an expectation that the deal will add value for both parties: I get important information that allows me to make an informed decision, and the service provider gets reimbursed for the expertise that gets me there.
When you get free advice on internet forums from people with unexamined expertise, unknown background in the field, often with anonymous identities, you have to rely on whether what is posted "sounds reasonable". Which is of course nuts, because you would not inquire, if you could tell fact from bullshit.
Please don't kill the messenger. But this is no way to buy a $20k mic. Hire an authenticator, get the authentication in writing, and make an informed decision, based on that expertise.
Considering the low cost of what most authenticators charge, a pre-purchase authentication is dirt-cheap insurance that could save you from a foolish purchase, or give you peace of mind in finding a true classic.