The way I remember is that 1 year -> 1 tree ring is more like an ideal than reality. You can have a series of cold summers with no growth or warm winters with

The way I remember is that 1 year -> 1 tree ring is more like an ideal than reality. You can have a series of cold summers with no growth or warm winters with continuous growth. Either can lead to many years -> 1 ring. Or you can have multiple warm/cold periods in one year in which case you can have 1 year -> many rings. As a result the samples that are used for dating need to be carefully chosen, and this has not been done independently of the other sources of data. I also remember it was difficult to find the raw tree ring data (all the images they tried). What was available was only some final data on ring widths, this made me question their assessment that alignments of the various tree ring datasets could just be due to chance similarities.