4 dictionaries give "at face value" a slightly different meaning, what should I do? [duplicate]
Solution 1:
You might consider the phrase face value for its basic meanings:
Merriam-Webster face value
1 : the value indicated on the face (as of a postage stamp or a stock certificate)
2 : the apparent value or significance
if their remarks may be taken at face value
Any of the definitions cited in your question can be seen as valid in the light of the basic meaning of the phrase. In some cases, a mention of face value (meaning apparent value or significance) means that the actual value may be different from that.