I could not confirm what your colleagues said.
Usually I track this using a url parameter if I am using the same page for different things. Are you doing that?
When you say the conversions are different - they can be tracked differently:
- AdWords Conversion - usually this means a click on the ad
- Marketo Conversion - usually means form fill out, so this would be less than AdWords
Would Adwords or GA track the full form fill out for you?