Paul McCartney Linda Eastman
In the well defined terms of the two degree rule (which is a tool used to enable statistical evaluation of both progressed and natal Venus aspects), there is nothing in this relationship that confirms the idea of progressed Venus synastry. This means that while we have found close progressed Venus aspects (and close aspects from progressed Mars and the Sun to natal Venus) to be especially prevalent in relationships, meaningfully so in fact, this is not the case in this relationship which is a very unique example of closeness, compatibility and success over a long period. While we could infer from this that progressed Venus synastry is not true in all cases, we could also infer that it is not bound by the two degree rule, especially where there is sensitivity to musical and poetic inspiration. For this reason and because Sir Paul is known for his ability to "pluck pretty good tunes from the ether", I think it is worth considering a long-period trine between his progressed Mars (in cell C7) and Linda's progressed Venus ( in cell D6) as the primary relationship indicator in this instance. This means that we have to allow a seven degree progressed Venus aspect in this case. If we look at this aspect on a collision graph, we find it has a curious reflexive quality:
The aspect reflexes on an exact point in late 1982. Either side of the exact point we have a distance of 6.9 degrees from the date they moved in together (October 1968) and the date of Linda's death (April 1998). I haven't done enough research to tell if this is an unusual occurrence in long term relationships, but in this case, the facts fit the aspect.
There is another important and interesting theory concerning this relationship which was first noted by a member of the AstrologyAmor relationship astrology group (on Yahoo Groups). Paul and Linda's natal and progressing Venus' were at a contraparallel (this is like an opposition of declination rather than longitiude) and Linda's progressing Venus was contraparallel Paul's natal Sun.
This is a synastry matrix which shows degrees of declination rather than longitude. Angles of declination add an extra dimension to synastry, and this dimension is literally the third dimension of up and down or celestial latitude. Planets make angles which we measure in a flat circle as aspects, but their motion also takes them up and down in the ecliptic plane. These connections in Paul and Linda's synastry will act in a similar, but not necessarily identical way, to conjunctions according to modern practitioners (although some older sources regard them as similar to oppositions) of the same planets.