Over the years I've heard K.N. Rao encourage students to apply the principle that when a planet is retrograde it will also aspect from the previous sign. This may seen rather shocking if you've never heard of this before. This would mean that when Mars, Jupiter, and Saturn are retrograde they would aspect 8 of the 12 houses, including the house they're in. This principle does not apply to Rahu and Ketu since they're almost always retrograde.
Recently, I asked K.N. Rao about the origins of this principle, and his reply was, "It is Bhrigu astrology, neither Parashara nor Jaimini. It is to be applied only to transits. It is given in Bhrigu according to late K.C. Saxena who did excellent research in this branch. He asked me to use it both in transit and the birth horoscope. I found it working very well in transit but I feel that we may overstretch our interpretation if we use it in birth horoscope though it is permissible according to late K.C. Saxena."
Not too long ago I came across a chart that dramatically showed the validity of this principle with regards to its use with transits. Here's the chart of a woman who was married in April 1993 in her Rahu-Venus-Saturn dasha. Rahu dashas are known for often giving marriage, while Venus is the karaka of marriage, and Saturn is her 7th lord. Now see her chart:
On the day she was married, April 2nd, notice how Saturn, her pratyantara dasha lord, is transiting through her 7th house. This is certainly a clue by transit that this could give marriage. However, notice that Venus is in Pisces and retrograde, giving it an aspect also from Aquarius, her 7th house. In addition, notice how Jupiter is also retrograde in Virgo, giving it an aspect from the previous sign of Leo. With Jupiter from Leo aspecting to Saturn in Aquarius, this means that the double transit of Jupiter and Saturn is taking place in her 7th house.
Transits April 2, 1993
For an event to manifest the fruits of what the dashas are indicating, there usually needs to be additional support from the transits. If you excluded the retrograde aspects of Venus and Jupiter, then only Saturn would be aspecting her 7th house, which is questionable whether this is enough from a transit, especially because Saturn is a malefic. But with the additional aspect of the two great benefics this event can be much more easily explained logically.