Here are things that indicate that a sealer is present in some degree. Compare to a piece of UNINSTALLED surfacing from the same batch, or as close as possible:

• Look for some degree of gloss (consistent or patchy) on the floor that is not seen on the raw material. Some sealer create gloss.
• Compare water drop absorption on the floor against the raw material. Significantly slower and/or uneven absorption on the floor indicates something below the surface. This is usually a sealer, but check the page in FAQ Sealers for dealing with oils and waxes. This video will give you an idea of what to look for: To determine absorption range If you determine a sealer still remains to some degee, it needs to be removed. Old sealers will potentially interfere with the penetration and bonding of a new sealer.

If the surface is stripped as much as possible, see "Redoing a Previously Sealed Surface" for the necessary testing and considerations.