The exact dates of publication of Byrd's mass settings remained unclear until 1966, when music historian Peter Clulow subjected the surviving partbooks to close bibliographic analysis.

Tracing patterns of wear in the woodblock initials at the head of each movement led him to conclude that the printing was the work of Thomas East, a noted music printer in Elizabethan England.

Clulow's conclusions can be summarised thus:[2][3] Following the religious conflict of the English Reformation, settings of the Catholic Mass were highly sensitive documents and might well have resulted in the arrest of anyone caught with them.

The native tradition of Mass composition had lapsed after 1558, when the Catholic queen Mary Tudor died and the mediaeval Sarum Rite was officially abolished in favour of the Anglican English liturgy.

However, Mass continued to be celebrated illegally by the English Catholic community, often with considerable pomp and under constant threat from spies and paid informers.

To that extent they conform to the liturgy as required by Mass celebrations by the incoming missionary priests, who had been trained on the Continent at the English Colleges in Douai and Rome and returned to England to minister to the faithful.

[6] The Gloria, Credo and Agnus Dei all begin with a two-part semichoir section, a standard feature of early Tudor Mass cycles.

It is built on a restless suspension figure, which generates a chain of overlapping entries, building to a climax before resolving onto a luminous final major chord.