Lead Was Created field and filter anomalies

[Anonymous]

I've noticed that leads that have been merged and have multiple "New Lead" activities don't have a value displayed in the Lead Create Date column most of the time.  Has anyone else noticed this or know why there is no value?

Also I don't believe that the lead detail displays a Lead Create Date field (it does display the Created and SFDC Created Date fields) - does anyone know why it is not displayed?

Finally, if you use a Lead was Created filter, for leads created in the last quarter for example, Marketo will also display leads that were created prior to that, if they were merged with other records that had a New Lead activity in the last quarter - does anyone know how to exclude these from the filter results?

[Anonymous]

I noticed this as well.  Still shows up if a list is imported though

[Anonymous]

Clarification -

Please disregard my first question - the Lead Create Date is a custom column that I added in an attempt to expose the Lead was Created date (i.e. date the lead became known), and my smart campaign is not updating it in some cases. 

I still would like to know why you can filter on Lead was Created (which means it must exist), but it is not displayed in the lead detail, as a column in smart lists or in the Field Management. 

For my final question, I believe that when using the Lead was Created filter with leads that have been merged and have New Lead activities on different dates, you can exclude leads that also have a New Lead activity in a different period by adding a Not Lead was Created filter(s) and specifying the periods you want to exclude.