I am not the best person to ask about maintaining starter cultures and resurrecting dormant ones because I have been derelict with these essential duties, mainly because I jump around all over the place style-wise with my pizza making and have thus relegated the use of natural starters to the rear burner.
Some time ago, I posted my views on this subject at Reply 93 at http://www.pizzamaking.com/forum/index.php/topic,4693.msg46122.html#msg46122
. If you look at the following post, Reply 94, you will see Bill/SFNM's recommended method of maintaining underused starter cultures. With my underused starter cultures, I essentially followed Bill's method of culture maintenance but usually at room temperature rather than using my MR-138 ThermoKool unit (which came much later after this thread was started). For routine maintenance during active use of the cultures, I generally followed the same method as described by Bill at http://www.pizzamaking.com/forum/index.php/topic,6393.msg54767.html#msg54767
. I think you will find that there are many methods used by the members to maintain and resurrect starter cultures. It is difficult to say that there is only one method that works.