Hi Sundance. jcl can clarify for certain, but my understanding is there are at least 2 different things that can happen with the Z strategies at an upgrade:

1) The CR produced by a given slider setting can change. This can happen due to changes in the Z strategy, or different test period, or ???

2) The Z strategy can have changed so much that open trades cannot be properly continued (even though they may actually be continued leading to bad results).

This latter has happened a number of times over the last year+, and is what I was referring to. My recollection is the last time it happened was the 1.20->1.22 upgrade.

Upgrade instructions are only given from the prior version - i.e., there are no 1.20->1.26 instructions. So if one upgrade step is missed, I suppose that can cause even greater problems down the line when other upgrades are done...

Hopefully jcl can clarify all of this.