Getting the latest ETag before doing an update?

Currently my code makes a series of updates to some resource via a REST API but I also have some "rollback" logic that basically updates the resource to its original state before my updates if some kind of error happened. So in psuedo-code, the logic looks like:

public void doUpdate(Resource r) {
   // do a GET to get the latest eTag
   // make PUT call with eTag to do actual update

public void myLogic(Resource r) {
  Resource original = r;
  Resource copy = r.copy();
  try {
   // do something to copy
   // do some more things to copy
  } catch (Exception e) {
   // rollback to original version

This is a simplification of my actual code but my question is: Is it more correct to do GET before every update to get the latest eTag(as shown) or should I get the eTag once at the beginning and then "chain" the eTag I get from the prior update for the next update, including the rollback step?