You can download here my Master's thesis on the subject of rare (but not exceptional, on the face of it) prosodic phenomena.
Will update this post soon to give a few explanations, although I would really recommend to read my Introduction, as it will clarify the advanced metrics of those verses.
Back then I had no idea of how it worked, I learnt and explained, so if you read French, go on. If you need translations, please ask I will be happy to help.
After reading the Introduction, you can jump to the relevant part, which is:
Chapter III, pp. 62—74:
"Maintien de voyelle longue devant -t final"
An important point is the issue of syllaba anceps (I do not use this expression, but instead, I say "metric lengthening"). In very specific locations of the pattern of a verse, the syllable is indifferently long or short. If you know dactylic hexameters, you will see what I'm referring to, since the last syllable is indifferent. Same for the half-foots of pentameters.
However this way of calling it is arguably fallacious. Indeed, the syllable had to be pronounced always long, since otherwise, the metrics would be wrong: first, in even (i.e. not odd) — descendant, for that matter — verses, the non-stress must be of an equal length as compared to the stress; second, the final foot of iambic verses is a stress (since the rhythm is ascendant), and as a consequence, it also had to be always long.
Therefore, I do not use anceps or indifferent, but instead, I say "metric lengthening". Jean Soubiran and Jacqueline Dangel, I may add, had the same view on the matter.
Sometimes the -Vt group is in such a position. However, as explained in my work, such cases should not be excluded, but rather, we should understand a few things:
If Plautus put this syllable in this specific position, this is because he wanted its vowel to be lengthened.
People attending the show recognized the formal pronunciation.
The character pronouncing it was identified as putting some emphase into their speech.
The interpretive value of this effect was not trivial.
Of course, the argumentation would be considerably weakened if the lengthenings were always observed in a syllaba anceps. This is, I precise, not the case at all, as you will notice.
A small remark regarding the organization of the document.
Many times, several different prosodic "exceptions" are observed within the same passage. Therefore, sometimes you will have to jump to another section to get the analysis (since obviously, it would have been silly of me not to analyze each passage as a whole). This is the case for the first occurrence, abducat (770).
Also, please look at the little indication that follows each verse number, it will tell you what type of verse this is:
ia6 = iambic senarius
ia7 = iambic septenarius
tr7 = trochaic septenarius
an7 = anapestic septenarius
You will find the respective patterns for those types of verses on page 7.