I have written that it is sometimes necesary to splice data gathered from different sources, say when I suggested splicing satellite temperature measurements onto surface temperature records.
When I did so, I cautioned that there can be issues with such splices. In particular, one needs to be very, very careful not to make too much of an inflextion in the slope of the data that occurs right at the splice. Reasonable scientific minds would wonder if that inflection point was an artifact of the changes in data source and measurement technology, rather than in the underlying phenomenon being measured. Of course, climate sceintists are not reasonable, and so they declare catastrophic anthropogenic global warming to be settled science based on an inflection in temperature data right at a data source splice (between tree rings and thermometers). More here.