wallet – Trying to recover old BTC from a pre-2013 centralized exchange — I have my email, a 5-digit code and an MD5-like hash, but don’t remember the platfor

Back around 2012–2013, I purchased some Bitcoin on what I believe was a centralized exchange. I never touched them since, and I’m now trying to recover access.

Here’s what I still have:

• My old email address used to register
• A 5-digit code (possibly a PIN or account identifier)
• A 32-character string that looks like an MD5 hash or similar cryptographic fingerprint — it’s too short to be a private key, and contains non-hex characters, which suggests it might be a platform-specific token or session ID rather than a standard hash

I do NOT have:

• The name of the platform (I genuinely can’t remember)
• A seed phrase or private key
• A wallet.dat file (as far as I know)

My questions:

1. Could this MD5-like string help identify which platform I used?
2. Is there a way to trace back which exchange was associated with my old email, based on the type of identifiers they used at the time?
3. What were the most common centralized exchanges before 2013 that I should try first (Mt. Gox, Blockchain.info, Coinbase, BTC-e…)?

Any guidance would be greatly appreciated. Thank you!