I am of the opinion that a lot of "being current" is the ability to recall and apply in a timely fashion, what you were properly taught some time ago.
Short of actually hiring an instructor to fly with me in my plane, I take every opportunity I can to have a check ride. I occasionally fly different types of light aircraft for design change approval test flying, and when I can get a check ride, I certainly do. Sometimes it does not work out though. Test flight of a modified light aircraft is generally permitted minimum crew only. Light plane = 1.
Last summer I was asked to test fly a modified Cessna 185 floatplane (including spinning it at gross weight and both C of G limits). I asked for a check ride, (hadn't flown one in nearly a year) but it was not possible. I sure spent some careful time doing a review of everything before I took off. I took it all really slow and careful (I was not paying by the hour, what's my rush?), and had no skill problems (the plane was a different story, but it eventually passed).
Personally, I'm more worried about the affects of complacency on the quality of my flying, than failure of skill. Until you cheerfully retire from flying on your own terms, never think that you know it all, or have it all under control. Stay ever cautious - but not reluctant to fly. If someone is offering to let you fly their plane, and you feel okay to go, you're probably current. If you're uneasy about something, ask. There's nothing wrong with that. You're probably nearly current, and wise.
If it's your plane, "current" is between you, your insurer, and maybe government requirements. It amazes me how little annual flying my insurer will accept as being current!
If it's someone else's plane, I guess you have to follow their rules...
Cheers, Pilot DAR