Well I just got my renewal for the '74 Pig (first renewal) and there is no emissions test required.
I also saw the following in the Latest Scoop magazine, where they were quoting Harold Naber on policy TR-13-19, issued by CO Dept of Revenue for the county clerks.
There are 3 categories of collector vehicles:
Cat A: 1975 and earlier w/ no e-test required
Cat B: Post '75 vehicles registered before Sept 2009 which were grandfathered in when the 25-year eligibility requirement was discontinued. These vehicles are not required to pass emission tests upon renewal.
Cat C: Post '75 vehicles at least 32 years old and newly eligible for collector series registration. Emission tests will be required every 5 years.
I think I got collector plates for my '78 40 prior to Sept 2009, I'll have to check. In which case I would guess there is no e-test, based on the above...