RDavid's thoughts have made me rethink my idea, and so I have been trying to find clear photos of the jewel with the pendants -- without any success.
When the large bow was given to Princess Marina as a wedding gift the three diamond loops were attached. It seems from the photos I have seen that there were also 2 pendants attached to the lower two loops, but I cannot see whether those pendants were diamonds or pearls.
In the only photo I have of Princess Nicholas wearing the jewel the loops do not have any pendants.
I am still wondering if the diamonds in the loops attached to the bow are as large as the ones in Princess Alexandra's necklace, even though I realise that the diamonds in the loops might look larger if we could see them clearly from the front.
MarcA, the latest photos I have of this necklace show Princess Alexandra wearing it in 1960.
It maybe that she wore it later than this date. Hopefully, someone else will know.