What do I mean by your Apple ID becoming dusty? I mean that it is very easy to lose track of any of your accounts (email, banking, Amazon) if they seem to be working fine. Your browser or phone automatically logs you in, so there seems to be no need to keep up with your well-functioning accounts. Your Apple ID, like most of your other accounts, is actually two things: (a) An email and (b) a password.
The reason your Apple ID is different is that so much of your use of Apple products (even if you never buy any songs, apps, or movies) depends on your Apple ID. Your iPhone, iPad or Macintosh may be out of date because every time any of these devices tries to update itself, it prompts you for your Apple ID, and you don't know your Apple ID, so you forego updates (and possibly i-Cloud synchronization). Why? Because humans are not wired to keep track of more than a few arbitrary numbers or passwords. Until we have better methods (e.g., fingerprint, facial recognition, etc...), we are stuck with password logbooks.
I have seen this become increasingly important over the last year or so. So, what to do? Go to AppleID.com and check to see if your email/password combination works. If it doesn't, it is time to get out your little password logbook to see if you've forgotten your password. Now, be ready for Apple to send a 6-digit code to a secondary device in order to verify it's actually you.
Your Apple ID can get 'dusty' in the eyes of Apple. Best to keep it clear and clean by logging into AppleID.com and, once you know your Apple ID, log in to iCloud.com. The most honest representation of your Apple account, it's status, and what is synchronizing lie at AppleID.com and iCloud.com. Are your phone contacts synchronizing? Are your photos synchronizing? Do you have an old phone that you sold to Verizon that still shows up on your Apple account? You can check all these things at either AppleID.com or iCloud.com.
Gentle, no-nonsense advice and perspectives on technology.