When a vehicle is built a new, unused CJB is a "blank slate" until the build code software is uploaded to whatever the original VIN number is.
Once that VIN is "inscribed" to that CJB, that VIN is now carved into that slate.
There is no way to return a CJB to a blank slate (that I know of).
Therefore, if you have confirmed CJB issues, you'll need to source a new (blank) CJB and have the original build code uploaded, along with several other programming steps so the new CJB will recognize the current key fob(s).
If you're planning on changing the CJB yourself, understand that you will need to somehow get your car to a JLR dealer (or whomever else you'll use) in order to code it. The car will likely be immobilized until the new blank CJB is coded to your VIN. You might save a couple of hours labor to swap it out yourself but, unless you already have the relatively expensive JLR type diagnostic kit, you'll still need to pay someone to code it.
LRDirect.com can supply new CJB's for around $750 plus shipping. I've sourced several from them with zero problems.
Normally, the original build software files are pulled from JLR's network so you (or whomever) would need to have access from that source to code the new CJB.
There were some non-OEM third party aftermarket hard drives and/or cables/dongles advertised that were available for up to MY11 to provide some coding but often their claimed capability far exceeded their actual usefulness. Some of that was probably down to user [un]familiarity with the order and sequence of coding.
Depending on where you are located I would guess you're looking at a couple of hours' labor fees to code the new CJB.