How full did you fill your jars? Were they exactly to the ring? Also do you live at high altitude?
When you water bath your jars, how full you fill is an exact thing and can vary depending on what you are processing. Too little space at the top can result in the food being forced out the lid into your water. Too much space and air can remain to discolor or contaminate the food.
Also if you live above 3000ft water has a much lower boiling temp due to decreased surface pressure/atmospheric pressure and never really achieves a rolling boil, all cook times
should be adjusted accordingly.
If you can find a copy try the book "Putting Food By" authors Hertzerg, Vaughan, and Greene. Mine was printed in 1974. It has all the background how's and why's of canning, plus other preserving methods.