Particular verbal inflection classes in "The Proclamation of Henry III"

I'm reading a document about "The Proclamation of Henry III", in which the text is presented and a short commentary and glossary follow.

I'm interested in the survival of some of the distinct verbal inflections classes of Old English. In particular, I'm referring to the verbs "swerien", "makien" and "werien": I noticed that these particular verbs ends in -ien, while the usual suffix of the infinitive/subjunctive verbal forms in the text is -en.

In the glossary, I came across some dictionary-like entries, such as this:

swerien, 4, swear, 3 p. pi. subj. after hoaten ; ags. swerian inf., swerion subj. ; ge. sweren; p. 85. Str. 560.

Can you help me to find out what is special about these verbs?

The -ien ending was an Old English infinitive ending for a small subset of weak verbs. OE Swerien belongs to a specific class of Old English weak verbs called Class II weak verbs. The ones you are probably more familiar with are the predominant Class I verbs which follow an i-mutation pattern in which the -i- mutates (moves forward on the palate) and the resultant infinitive ending is -en. By contrast, Class II verbs did not undergo i-mutation and retained their characteristic infinitive ending -ien.

I looked at etymonline.com for a reference:

swear (v.) — Old English swerian "take an oath" (class VI strong verb; past tense swor, pp. sworen), from Proto-Germanic *swarjanan, from root *swar- (cf. Old Saxon swerian, Old Norse sverja, Danish sverge, Old Frisian swera, Middle Dutch swaren, Old High German swerien, German schwören, Gothic swaren "to swear"), from PIE root *swer- "to speak, say" (cf. Old Church Slavonic svara "quarrel"). Also related to the second element in answer. The secondary sense of "use bad language" (early 15c.) developed from the notion of "invoke sacred names." Swear-word is American English colloquial from 1883. Swear off "desist as with a vow" is from 1898.

I'm not sure about others, but I believe swerien has simply kept its Old Dutch -ien suffix (without changes).

Also this article has a good explanation on suffixes etymology (see Dutch section):