About scribal abbreviations and diacritics in digitalized book titles

Question

In the Wiktionary entry about philematology, there is a reference to this book. The title is copied (AFAIK, but I can't load the picture in the previous link so…) as in the cover, that is:

[Jacobus Herrenschmidius] (1659) Speculum φιληματολογίας [philēmatologías]. cùm Sacræ tùm profanæ: Per quæstiones aliquot ex variis multorum monumentis non minus ad voluptatem quam utilitatem S.S. Theologiæ & Philologiæ Studiosorum concinnatum operâ & studio.

My reaction:

1. That circumflex for vowel length (that's an ablative singular) is weird: why not use the standard macron for that?
2. Why on earth should we keep the &, which is just a scribal abbreviation, and not expand it to et?
3. What in the world is that grave accent for?

So here comes my question:

When digitalizing the title of a book containing scribal abbreviations and/or diacritics, should one keep them as they appear in the book cover, or expand the abbreviations and switch to the standard diacritics? (And also, what are those grave accents for? I mean, the only thing I can think of is vowel length, but that would be either a circumflex or an acute, why a grave? And besides, are those vowel even long?)

Another example of such a title can be found at carol, and is:

Piæ cantiones ecclesiasticæ et scholasticæ vetervm episcoporum, in inclyto regno Sueciæ passim vsurpatæ, nuper studio viri cuiusdam reuerendiss: de ecclesia Dei & schola Aboënsi in Finlandia optimè meriti accuratè à mendis correctæ, & nunc typis commissæ, opera Theodorici Petri Nylandensis. His adiecti sunt aliquot ex psalmis recentioribus [Pious Ecclesiastical and School Songs of the Ancient Bishops, Used throughout the Glorious Kingdom of Sweden, […]] (1582)

Answer 1

In my opinion, you should not try to "improve" the text acciording to your own whims, but represent the text as it is. This means keeping the ampersands and accents as they are.

To expand, the grave and the circumflex were used not primarily as length markers, but to provide some measure of grammatical disambiguation. In particular, although the circumflex did indicate a long vowel, it was not used indiscriminately to indicate any long vowel, but only those in certain circumstances, such as here in operâ, where it specifically signifies the ablative use. Similarly, the grave was often used to indicate an adverb or simply to distinguish some uses of common words.

It's a mistake to think of the macron as being "standard" - it has been (to the best of my knowledge) only used in teaching materials and dictionaries to indicate long vowels, not in regular texts, so it is a mistake to think of macrons and circumflexes as being equivalent.