As I get older, I find my perfect pitch is not so perfect as it was.
But these electronic tuners are not always as perfect as the makers want you to think they are. I've borrowed the bass player's tuner a couple of times lately, and I still find myself tuning a little bit sharper than the tuner - then the harmonica player turns up, and I'm in tune with him! What I have found in the past is that I can be distracted by hearing external music before I tune the guitar, then I tune it a semitone or a tone out of tune. As 50 approaches I'm not even a perfect interval out nowadays, but some fuzzy little bit off - and yes, I hate admitting it!