Hey there! That's a really smart question - dealing with 'new old stock' (NOS) Siemens components when the OEM support has ended can be tricky. Here's what I'd recommend based on what I found:

First, check for digital authentication features. Many Siemens modules have built-in manufacturer certificates with MD5 hash values. You can read these out using STEP 7 V5.5 software or web diagnostics tools. The certificate should match Siemens' official specifications - if the MD5 hash values don't match what's documented, that's a red flag.

Second, look for physical authentication marks. Genuine Siemens components usually have specific copyright entries, serial numbers, and manufacturing codes that are consistent with their production era. Compare these with known authentic components from the same time period.

Third, vet your supplier carefully. Reputable third-party suppliers should provide traceability documentation showing where the components came from. Ask for their authentication processes and whether they use advanced inspection methods like AI-based visual verification systems (Siemens partners with Cybord for this).

Finally, consider testing a sample batch first. If you're buying multiple units, test a few thoroughly before committing to a large purchase. Check performance against original specifications and look for any signs of refurbishment or tampering.

The key is combining digital verification with physical inspection and supplier due diligence. It's definitely more work than buying from Siemens directly, but with the right approach, you can minimize your risk significantly!