Most Daisy-chains have minimal statistical significance to the PCB's they represent. Each Patented* HATS²™ Single Via Coupon contains 7 single via nets. Each of these 7 Single Via nets can be changed to a daisy-chain to allow a mix of single via and daisy-chain net data to be collected. Testing 36 of these coupons in one HATS™ Chamber load, you get a sampling of 252 nets of single vias (or single via & daisy-chain) nets while being able to accurately track the initiation and progression of cracks/separation in each via and correlate to historical information with included daisy-chain nets.
To obtain "significance" from a sampling of vias in a daisy-chain, mathematical models can be used with assumptions made regarding the similarity and variability within the population of vias on the PCB's the daisy-chains represent. As an example, for drilled vias, a "similarly manufactured" population might be made up of 1200 vias drilled by a single drill bit. To obtain a result confidence of 95% with a margin of error at 5%, 125 vias from this 1200 via drill bit population would need to be in the daisy-chain. There are many issues with grouping "similarly manufactured" vias to form a via population from which to calculate a statistically significant sampling size, but however you add it up, the numbers of vias needed in a daisy-chain in order to get statistical significance just keeps going up.
Results from daisy-chains without hundreds of vias in them have little statistical significance to the PCB's they represent and are a statistical "feel good" measures at best and at worst, could be hiding small increases in resistance indicating structural via issues. In order to test the high resistance associated with a large daisy chains, the current flow through the daisy-chain must be reduced and with it accuracy and significant digits of resistance measurement. A 50% crack or separation in a single via would go un-noticed as it would only register a change of <0.0005 Ohms in a daisy chain resistance that might exceed 1 Ohm (.05% change). Even if we had several vias with a 50% crack or separation, we would only see noise in the measurements made.
Daisy-chains certainly have their place in via reliability testing to determine total via failure, but single via testing is the only way to track cracks/separations in vias from their initiation through to failure.