visid_high / low vs MCVISID
Hi all, it seems this question has been asked a few time but none of the previous questions have been answered so I wanted to try and get to the bottom of this.
We moved to the ECID service about 5 years ago and have data feeds set to export the data to AWS / GCP. We have multiple sites / apps and also performed the single domain migration in Adobe so we could use the first party cookies across all of our architecture.
Now the documentation states that visid_high / low are set by the MID which is read from the s_vi cookie and that concatenating them would give you a unique visitor ID, however other documentation states that the ECID is the most accurate way of identifying a customer which is stored as MCVISID in the data feeds.
To also set some further context all of the visitors I am analysing have been Identified by the ECID service & also have visid_high / low set as well.
My question is as follows:
A) Have I understood this correctly or am I barking up the wrong tree.
B) If I have why is s_vi being used when ECID is better
C) Which is the best ID to use for tracking visitors across our digital estate
D) Why do some ECID have more than one concat visid & vice versa
Really appreciate any help with this as I'm currently banging my head against a wall