I'm sure there have been those throughout history who have followed a modus operandi equivalent to what has been defined here as Modern Theravada
(i.e. those who were content with what had been transmitted via the suttas, who did not wish to build upon the corpus).
Of course it's those who built upon the corpus who have had their texts and interpretations transmitted through time, but it would be folly to neglect the existence of "suttavada" practitioners (for want of a better word) over the centuries simply because they're not identifiable through the advent of their own additional documentation (i.e. not identifiable via textual analysis) in the way the Sri Lankan Mahaviharans are, for example.
Most traditional/conservative standpoints are generally defined in terms of what they don't change/append, rather than what they evolve. David Snyder has often pointed out the irony that what is classed as "modern" is in some respects actually more conservative, in the sense of generally emphasizing the oldest strata of Buddhist teaching.
"Do not force others, including children, by any means whatsoever, to adopt your views, whether by authority, threat, money, propaganda, or even education." - Ven. Thich Nhat Hanh
"The uprooting of identity is seen by the noble ones as pleasurable; but this contradicts what the whole world sees." (Snp 3.12)
"To argue with a person who has renounced the use of reason is like administering medicine to the dead" - Thomas Paine