Reusing lifters

I've had cams that went from one engine to another and kept the lifters in order. Been pretty successful most of the time and then there were a few times I was short on funds to do it the way most people insist it should be done and used a plate of glass and some very fine grade wet/dry sand paper with oil and surfaced my own old tappets, it takes time but when you don't have money you have time. The only time I ever had an issue with a cam and tappet failure I managed to hang on to was the solid tappet Crane that went back in the block when the gear bolt cam loose to the point it went from one lobe to the one in front of it. and bent ALL of the exhaust valves. Then there was the time I simply swapped a set of valve springs into an old AMC because the factory springs wouldn't hold the valves close after oil pressure came up. I used a set of old small block MOPAR springs in the AMC, it was a few months later one tappet went all the way through the bottom and dumped oil, Obviously that cam was done for. The engine started backfiring and blowing vacuum hoses off at every port. The most important point with flat tappets is having ZDDP in the oil at all times ! Even after break in. Removal of ZDDP is the main reason older engines are so rare anymore. Of course once break in is over as in several thousand miles cam failure is far less likely to be an issue, but still a possiblity.