When taking about 18 Explorer Scouts on a 2 week cycle trip through Denmark we checked all the bikes over, had a mechanic in one evening to check the bikes over, and then once on tour proceeded to get a typical half dozen puctures a day.
The bikes were begged, borrowed and stolen, several of the nicer ones were old road bikes that had obviously belonged to Fathers, Uncles and probably Grandfathers and whilst mechanically sound still had the original 1960's or 1970's tyres which looked fine
Lesson learned is tyres have a life of perhaps 10 years in the shed, so we should have bought a job lot of tyres in the UK and replaced the lot
Unfortunatly we had to do this in a small town in northern Denmark where we cleaned out the shop of every suitable tyre they had and spent a day changing nearly every one