Video Impressions issue

It sounds to me like your eVar v12 is configured with a Visit level expiry, meaning that there are pages were the v12 is not being explicitly set, but the value is carried forward to contexts where the video event (event12) is being fired.

Props are always Hit level attribution

Events are also Hit level attribution

eVars are configurable, but default to Visit level attribution

Let's look at an example:

• Page 1
  • Prop is set (s.prop1  = "page1")
  • eVar is set (s.eVar1 = "page1")
  • event "eVar1 Instance" is triggered (this is an automatic event tied to eVar usage, not a custom event)
• Page 2
  • Prop is set (s.prop1  = "page2")
  • eVar is set (s.eVar1 = "page2")
  • event "eVar1 Instance" is triggered
• Action 1
  • Prop is not set (value is null)
  • eVar is not set (value however is still "page2", since the visit level attribution carries the value forward)
  • event "eVar1 Instance" is not triggered (this only triggers where the eVar is explicitly set, not where the value is maintained)
• Page 3
  • Prop is not set (value is null)
  • eVar is not set (value however is still "page2", since the visit level attribution carries the value forward)
  • event "eVar1 Instance" is not triggered (this only triggers where the eVar is explicitly set, not where the value is maintained)
  • event "event1" is set (this is the custom event)
• Action 2
  • Prop is not set (value is null)
  • eVar is not set (value however is still "page2", since the visit level attribution carries the value forward)
  • event "eVar1 Instance" is not triggered (this only triggers where the eVar is explicitly set, not where the value is maintained)
  • event "event2" is set (this is another custom event)

You can see how many more places that eVar1 has a value, and that it pairs with both event 1 and 2, whereas the prop does not.

eVars were originally supposed to be use for conversion attribution.. i.e. set a value, have that value maintain through the visit to pair will any/all conversions, or expire after a specific conversion, or expire after a set time (like a month or a year)... the value would remain until expiry, or until it was overwritten. For example, an internal campaign... I click on a campaign and track "campaignX"... that value will remain on all hits until the end of the visit.. so that when someone makes an order, I can correlate the "order" to my eVar and see that CampaignX was the last touched internal campaign that drove the purchase.

Now, eVars are used for so much more, particularly since they have a 255 character limit (as opposed to the 100 character limit that props have)... 

But, when you are using eVars, you must be aware of the scope / expiry in use, or you will be confused by how your data correlates.

My two cents... if you are tracking "Page URL" in your eVar, that eVar should be set to "HIT" expiry. If for some reason you need to see previous URLs in the path to a specific event, you can use the custom attribution model to look at "last touch" or "participation" etc....  but this seems like it would be a rarely used scenario.