Can data from sites with either universal or classic analytics be sent to the same property?

Question

We have a number of sites that feed data in to a single property. Currently, these all use ga.js to record data but we would like to upgrade to analytics.js as soon as possible. However, as we have a number of sites, ideally we want to be able to upgrade incremently, one at a time. For example:

Current: SiteA (ga.js) + SiteB (ga.js.) + SiteC (ga.js) = Property1

Phase 1: Site A (analytics.js) + SiteB (ga.js) + SiteC (ga.js) = Property1

Phase 2: Site A (analytics.js) + SiteB (analytics.js) + SiteC (ga.js) = Property1

Etc.

Is this a viable option? Will there be any noticeable impact on our data?

Note: As of yet, we don't have proper cross-domain tracking in place, which is part of the reason we want to upgrade to universal analytics, so this can be disregarded.

Answer 1

Resolved: turns out it was the AdBlock chrome extension.