Tolkien surname older than adjective tollkühn and the problem of "Saxony"

Source: DWDS - tollkühn

The first time we can find the Tolkien family name in the sources is 1378 (Heynike Tolkyn) and 1418 (Ritter... Tolkin) (1).

The first time we find the adjective tollkühn 'sehr kühn, verwegen; foolhardy, rashbold' in the sources is much later, in the seventeenth century. From the sixteenth century there come the form ein toller küner man. What is interesting in the Middle Low German (2) from the fifteenth century there can be found the form dulkȫne 'unüberlegt, unbesonnen' so different from the name Tolkin and Tolkyn of that time (3). Middle Low German was also used on the same territory where the first Tolkiens lived (we can find links between the first Tolkins and Tolkyns, and the Tolkiens from the seventeenth and eighteenth centuries).

We can assume that in the time where we find the name Tolk/Tolkin/Tolkyn (the 14th-15th c.) there is also the noun tolk 'translator', but the adjective 'foolhardy' has the form dulkȫne which is very different from the personal name Tolk/Tolkin/Tolkyn.

The map shows the territory where Low German was used historically. And because Low German is also called Low Saxon, maybe Tolkien's words about "Tolkiens coming from Saxony" refer to the linguistic territory of the "Saxon" language? 

What is your idea?

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(1) Regesta Hist. Dipl. Ord. S. M. Theut., II 1052 and II 1934

(2) Middle Low German served as the international lingua franca of the Hanseatic League. It was spoken from about 1100 to 1600. Traces of the importance of Middle Low German can be seen by the many loanwords found in the Scandinavian, Finnic, and Baltic languages, as well as standard German and English.

(3) In Middle Low German there is a noun of the Baltic-Slavic origin: tolk, tollik (Schiller-Lübben 3, 571ᶜ), 'dolmetsch, interpres; translator, interpres'; (Dief. 305ᵃ. nov. gl. 219ᵇ. Stieler 2249, pers. reisebeschr. 1, 4, 6, entlehnt aus lit. tulkas, lett. tulks Kluge⁵ 74ᵇ. vgl. Freytag ges. werke 16, 429).