A major factor which has both a cause and an effect relationship to this matter of sequence is the morphology of Old English. The extensive inflectional system signaled relationships for which we now rely solely on word order. We would call this a run-on construction. There is no way to assess the size of the word list in use beyond what has been written and has survived to the present. The vocabulary expanded from two general sources, a native source in compounding native words, extending their usefulness through prefixes and suffixes, and extending the function of some words through a functional shift, and a foreign source which added words borrowed from other language groups including a few from Celtic and Scandinavian and a larger number from church Latin.
Words change meaning over time, sometimes slightly, sometimes dramatically.
We can recognize in Old English texts words that are still in use today, but it does not necessarily follow that these words meant then what they mean now. It is safer to assume that the meaning of the word has shifted somewhat, and perhaps very significantly. A significant body of writing in Old English, both in prose and in verse, is available still. Old English was the first vernacular language to develop a good prose style. Old English verse, some 30,000 lines of it, is about evenly divided between epic and shorter verse forms.