Macbook Pro Retina 2015 Lost firmware password and no receipt

No one knows what the passwords could be, and whomever originally purchased them doesn't work here anymore, so I don't have access to the receipts.

Without original purchase receipts you are more or less at a dead end. Your greatest chance for success is to track down whoever purchased those Macs. Once you do that, cajole, beg, plead, bribe him or her for assistance.

For one story with a happy ending, read Locked out of AirMac Pro problem or Firmware issue?? - Apple Community. It's a long story.

Erik Rosenbluh wrote:

Hi,

I rescued a couple 15" 2015 Macbook Pro Retina's from the e-waste closet at work. I want to wipe them clean, but they both have EFI Firmware locks on them. No one knows what the passwords could be, and whomever originally purchased them doesn't work here anymore, so I don't have access to the receipts. Is there anything I can do besides chucking them back into the e-waste closet?

Thanks

Here is a 2015 article—

https://osxdaily.com/2015/01/28/forgot-mac-firmware-password-what-now/

Forgot a Mac Firmware Password? Don't Panic, Here's What ...

more—

<block quote>

In 2011, however, Apple added an important change to the system: the firmware password was moved to a separate programmable controller from Atmel. This component contains lockable flash memory to store the password and requires special programming with identifier numbers for both the Mac's motherboard and the Atmel chip to access and reset it.

Since the controller is an independent component, the only way to bypass it is to manually remove it from the motherboard, but this requires highly precise reflow soldering tools and techniques.

</block quote>

ref: https://mac-optimization.bestreviews.net/bypassing-efi-lock-on-your-mac/

I assume you mean the receipts to show original purchase. You also have to prove via ID you are the original buyer ... two bits of information

As to back in the closet ... that's about it. Their fate was decided long ago.

Having said that, have you tried anything to reinstall the OS? I'm a little surprised a business doesn't have some sort of recovery plan or agreement with Apple. The business is, after all, the owner and buyer.