I see your point. Some of our measurements are counters and interpolate missing data via certain rules. We store these interpolations in a separate table with exactly the same format and join the two tables directly when querying the data. Since the real value always takes precedence over the interpolated value this is just a COALESCE(realmeasure0000, interpolation0000) statement.

This is super fast when taking advantage of postgres' partition-wise joins.