With an eye towards the special needs of touring cyclists, a quick note on the commonality of tire 'sizes': Down at my local big box stores, one can readily buy 700C (ISO622mm) tires - in a width suitable for common hybrid bikes. These 700C tires will not fit on your Pinarello Dogma F12 nor will they shod your 29er+ mountain bike, both of which also use '700C tires'. My LBS inventories 27.5" (650B) tires for mountain bikes that would not be suitable for randonneuses, even though all use ISO584mm tires.

I would never argue that the old days and the old ways were better, but if you have a bike that uses 27" (ISO630mm) tires, I think you'd be hard-pressed to find a 27" tire that was NOT suitable for your rims & clearances. Same with 26 x 1 3/8 (ISO590mm).