I’m always happy to help 
The complexity and ambiguity of EHR data coupled with the lack of clear conventions increase the complexity of ETL’ing to the OMOP CDM. If you send me your email address, I will add you to the EHR WG invite. It’s an open meeting, but I find it easier to have an invite on my calendar instead of digging through the forums or finding the meeting details on the OHDSI WG meeting page.
Correct
Well, there are many ways to skin a cat and many ways to ETL observational healthcare data to the OMOP CDM
However, there are not any clear conventions on how one should set an Observation Period for EHR data. And I think it is time we decide as a community and write it down (@Christian_Reich I’ll add this to your ‘to do’ list since you’re working on the conventions now ) In general, folks with EHR data set the start date of the Observation Period to the start date of the first event for the Person in your data. The end date is the end date for the last event in your data. UNLESS you know all the Persons in your data will always be seen at your hospital/clinics/care sites. Then you would start the Observation Period with their enrollment date or registration date and end with their exit date from your system (if you know they left & now receive care elsewhere) or the date of the last data from your EHR system (if you believe they would still seek care at your institution) or the date of the last clinical event (if they may have received care elsewhere). Here is some discussion on the topic. Documentation of the decision and reasoning behind it is important!
Cheers,
Melanie