Kevin Lowther writing in the United States Stamp Specialist (January, 2017) New Technologies Invite Collectors to Resubmit Items for Certification states "Expertizing services now have more advanced means to examine items that may previously have defied ready identification or were misidentified." He continues with "Because of the improved technologies available, APEX Director Mercer Bristow suggested to me that holders of items certified more than 15 years ago should consider submitting them for recertification." NOTE: Mr. Bristow has since retired from APEX.
Further, John M. Hotchner, writing in Linn's February 3, 2017, When you should consider resubmitting a previously expertized stamp quotes Mr. Lowther and adds his own endorsement regarding updating older certificates.
I think this is reasonable for some items, but is silly for others. Use sparingly, it make sense. If a stamp has a cert that states sound and genuine, and it no longer looks sound, do you think anyone is going to resubmit for a new cert? (While they should in that case, no one will)... Mostly because collectors like to "show off" their collections... and a lower valued cert doesn't excite. So if you're holding the stamp, fine, but if you want to BUY it, then the cert may be worth re-investigating.
Now, certs on stuff we know to be "wonky", sure, a re-submission works. I'm sure that none of the certifying bodies are "motivated" to increase their submissions (i.e. sales). No, none of them would want to do that...
Regarding the above opinions on second opinions and recertification: 1. Medical opinions —another tier of that story relates to whether the second opinion is sought in a lateral move ( community to community) or vertical (community to university). It is not that unusual for a second opinion vertically to start with the assumption that everything done in the community was wrong without regard to who did the original evaluation, what his or her background/qualification are, etc. this is an unfortunate assumption but it is in keeping with human nature. I suspect it probably operates within the university level as well—for example, an original workup having been done at an osteopathic institution now getting a second opinion at MSKCC, Hopkins, Yale, or MD Anderson.
2. Recertification based solely on age of current cert. unfortunately this impact on data that is difficult to know. If an elderly collector bought a classic in 1967 and had it certified at that time and then stored it in a safe deposit box until now, then the only reason to get a new cert would be if it was a candidate for a grade of 90 or above. Of course how would you get this history. By contrast, if an item has been continuously traded at auction or privately over the past 20 yrs let's say, at each point due to handling and repeated examination there is the potential for change from the original condition. But again, except in a very small % of collectibles of all kind, how many of us have an extensive provenance on any of our items even to the extent of knowing, not who the prior owners were, but even how many?
With stamps, I am not sure why people even care about provenance. It is a sellers tactic to excite you about previous ownership, as if a stamp owned by someone famous in philately is now worth more simply because they owned it. It should not change anything about the stamp valuation. If, for example, a cert comes back as a certified clean 100% gem, who in the world cares who owned it before you- Sam at the corner consignment shop or Bill Gross?