There is nothing called sure fire way, even if you see the Purchase order or check the material certificates of the valve especially When you are dealing with valve without identification.
Even if you have identification and are able to trace to certificate and the certificate say it is NACE compliant, the extent of your sure fire based on the certificate. The level of assurance you have now depends on the reliability of the valve certificate issued by valve manufacturer.
I have come across many occasions (At least once in one project) where the top valve manufacturer (Although they have all fancy ISO 9000 and API 6A certification) fails after start up and when one digs we find the stem material which is supposed to be 316 is 718 or when the stem is supposed to be 410S it is XM-19 etc. Right now i am dealing with top DBB manufacturer from Italy and France (Shell Approved, Exxon Approved, Supplies regularly to Total, BP, Oxy), fails (No China material) all the material had traceability (Good stamp, good West European certificate for material and valve), yet in PMI (Which was done after failure of over 50 valves), we had problems.
So there is nothing called sure fire. It depends on what is going to give you assurance and how much you would like to see. In any case, it is my firm view that valve NACE compliance is non issue (So long as the valves are bolted/ flanged and not welded to piping), since if it fails, you can always replace it with relative ease.
The focus for NACE compliance is to be given on welded item and welded valves, because, if it fails after start up, we have many operational issues (as compared to flanged valves). I am not saying flanges valves can fail and it is OK, i am saying, at the time of final walk through, one can focus more on gross issues. If one wants to increase the level of assurance then there are methods that works reasonably well and those give adequate assurance. Despite this, as i told you earlier i deal with failed valves.
This is what i feel about walk through. It is my view that one can identify gross error, during walk thorough, if one goes into finer details, it is no longer walk through. It is dig up.
If you want less than sure fire method with reasonable assurance, i can share. First step is to identify the lines that you consider critical and do the exercise only on those critical.
Conduct N2 + He leak test at operating pressures, it will take care of the leak from gland of valves. Even of the internal non metallic seals and parts are not OK and valve leaks, it does not leak to atmosphere, so much you have assurance when you check the for leak from gland area.
Have a PMI machine and some emery paper and WD 40 and some thinner, chalk, wire brush and magnet and Ferrite meter, small grinding machine (File) You need 2/ 3 person team to walk with you.
Take 2 walks, one focusing only on valves and another general.
By the time you walk through you would have gotten familiar (From the shapes of the valves and the hand wheel color or other unique feature, who is the manufacturer of the valve).
On the lines that are considered critical, select one valve per manufacturer in the line and spend some time to check for punch mark or embossing on the body. If the material has identification, and if is listed in NACE/ISO 15156-3 (For high alloy) and NACE/ISO 15156-2 (A 105, A 106, A 333, A 234, A 420 CS and LTCS general valve material) need no further verification as these do not need any special blessing to be called as NACE compliant, they are automatically compliant.
If there are no marking, then perform PMI and verify as above. Here your assurance reduces since NACE gives specific heat treatment recommendation for some of the alloys, if you do not have punch mark, a material chemistry may be OK, but may not be OK from the heat treatment point of view especially for high alloy material. Hence you should know there a reduction in assurance.
If you are in the beginning of the project, there is much easier way, if you are not tired and want hear about that, then there is a simple way which is very close to sure fire.