I've personally worn down chainrings enough to get full-circumference chain slippage. Including the big ring! Sometimes you can see this by pressing down on the crank while watching how the chain reacts... if the chain begins "climbing" the teeth under load, trouble's brewing. When it does happen to me, it's usually at a very inopportune time, such as trying to pull away from a stoplight very fast with traffic stacked up behind me. Dangerous and embarrassing to have the bike suddenly "go into neutral" while trying to accelerate. Adding a new chain to the mix will concentrate the problem because only some of the teeth are getting proper loading.
Anyway, after 20 years, those rings have definitely delivered a good service life for your money
