Were national assembly MPs ever sent as MEPs without an election after 1979?

Question

In the context of a Brexit delay, an article in the Guardian mentions that

The prospect of a lengthy delay has been made more palatable after the UK’s advocate general in the European court of justice, Eleanor Sharpston, described claims that the European elections in May would be an “insuperable obstacle” to a lengthy extension as “oversimplified and fallacious”. [...]

Sharpston said the UK could extend the mandates of its MEPs “who have already been democratically elected and who have been sitting in the current European parliament” or send “nominated MPs from the UK, rather than directly elected MEPs, to participate in the European parliament during that period”.

Is there precedent in the EU for MPs from the national assembly of a member EU country to be sent as MEPs without an[other] election specific for the latter purpose? Well, the answer to this question is somewhat trivial yes: that was actually the case when the UK joined the EU (well EC)... and the situation lasted surprisingly long—six years, from 1973 till 1979. But the catch is that the 1979 election was the first direct election of MEPs across the EU. So it makes more sense to ask: were national MPs (from a EU country) sent as MEPs without a dedicated EU election after 1979?

Answer 1

It did happen more recently when Romania and Bulgaria joined the EU (in 2007):

Another option would be to appoint national representatives in lieu of MEPs until the end of the Article 50 period. This would closely resemble the process that Romania and Bulgaria followed when they joined the European Union in 2007.

Although Romania and Bulgaria joined on 1 January, they only held European Parliament elections in May. In the interim, they appointed national representatives, who had served as observers to the European Parliament from September 2005 to the end of the following year. In line with their accession treaty to the EU, the Romanian Parliament appointed a total of 35 observers from the governing and opposition parties; similarly, the Bulgarian Parliament appointed 18 observers. When they joined, the number of seats in the European Parliament increased from 682 to 785. Likewise, the UK Parliament could appoint members as national representatives to the European Parliament.