Almost in all modern sources concerning the Տօնացոյց of Simeon Catholi­cos it is mentioned that Simeon Yerevantsi has divided Տօնացոյց into two parts – two volumes. The source of all such statements is the preface of the Տօնացոյց published by Simeon Catholicos in 1774 in St. Էջմիածին.
In contrary, we see that this Տօնացոյց is not divided in essence: it is pub­lished in one volume, it has general numeration of pages and the contents of two "volumes" continue and supplement each other. 
Analyzing this Տօնացոյց and other similar books published during pre­ceding hundred (and more) years we see that Simeon Catholicos has first united the traditional Տօնացոյց with another important book concerning Armenian ca­len­dar called Պարզատումար that was widely used that time. After this unification he has formally divided the newly formed unite into two volumes according to the original contents of the former components. Thus, Simeon Catholicos has of­fi­cially changed the traditional canonic structure of Տօնացոյց firstly com­po­sed and determined in early V century by the Catholicos St. Sahak Պարթեւ. 
The Catholicos Simeon has also made changes in the list of holidays and the priority of the feasts. All the changes made by this reform take aim to raise and emphasize the value and the authority of Armenia and Armenian Church.