Regarding the SEO, I wouldn't expect it to be an issue, as Google have enough common sense to realise that, if the two URLs you have shown returned the same content, that for all practical purposes the URLs the same to a human.
In fact some webmasters/developers will write brief rewrite rules to append or remove the slash because "it looks nicer".
These rewrites may be internal HTTP server redirects (which are not visible to external user agents) and for Google to "expect" webmasters to code a dedicated redirect and corresponding round trip communication between server and user-agent which "announces" a redirect (and therefore a canonical URL) - e.g. a HTTP response with
30x and a "Location: [old URL except with a slash on it]" - and punish those who dont - doesn't make much sense.
However I don't work for Google so I couldnt say for sure - I just personally would bother with it, and you can always specify the canonical URL using the "rel" canonical tag.
If the URLs deviated any more and still returned the same content, e.g.
Then I would clean them up and specify canonical URL.
In my experience - with PHP - if the
REQUEST_URI (portion of address following the
HTTP_HOST which contains the
REQUEST_URI and the
QUERY_STRING) has a slash or not - PHP doesnt seem to care - the slash will be captured in the
$_SERVER['REQUEST_URI'] array key and the query string in the