In this section I focus on two types of studies. Firstly, those which treat some differences between the whole set of plays, and secondly, those which deal with some particular plays, which would seem to belong to different periods and authors.
Already on the ground of the percentage of the shloka metre, Jahagirdar is able to divide the plays into two main groups, A and B (1931:42). Furthermore, considering the opening verses, the bharatavâkya and the sthâpanâ, he is able to split the high-percentage group, or group A, into two more groups (1931:43). His groups are the following. Group A1 consists of Svapnavâsavadatta, Pratijnâ and Pancarâtra. Group A2 consists of Madhyama, Dûtavâkya and Dûtaghatotkaca. Group B, or the low-percentage group, finally consists of Avimâraka, Bâlacarita, Karnabhâra and Ûrubhanga. In fact, this scholar was the first who used a systematical linguistic approach in examining the several plays. In addition, Jahagirdar (1931:43) observes that in the Karnabhâra a prastâvanâ occurs instead of a sthâpanâ, so in this respect, too, the group is not homogeneous.
The play Avimâraka might be late, as it would be based on Dandin's Dashakumâracarita from the 7th century A.D., and therefore must have been written much later than Bhâsa's Svapnavâsavadatta (Pisharoti and Pisharoti 1923-25:108). Keith disproves this with the argument that the Brhatkathâ, on which both the Dashakumâracarita and the Avimâraka are based, was written a long time before Dandin (1923-25:295). In addition, the fact that they both treat the same subject does not prove at all that the one is a compilation of the other. If that would be true, then the numerous Râma dramas would be nothing more than compilations of each other (Shâstrî 1923-25:629). Masson supports the idea that the elements which seem to fit badly into the play belong to the older legend, that is, a legend closer to the lost Brhatkathâ of Gunâdhya (1969-70:74). This would imply that the Avimâraka, or Avidâraka (1969-70:65) may be old after all. However, Trautmann (1981:338-340) draws attention to the clear Dravidian kinship system as found in the Avimâraka, which is lacking in all the texts derived from the Brhatkathâ, except for the Kunâla Jâtaka from Sri Lanka. If he is right, the Avimâraka at least must have its origin in South India, but the date still remains uncertain.
Barnett assigns a late date to the group, based on the Pratimâ, Act 5, or more precisely, the prose between verse 8 and 9, spoken by Râvana (ed. Devadhar 1962:296). According to him, reference is made here to the Manubhâshya of Medhâtithi from approximately the tenth century A.D. (1923-25:520). Keith (1923-25:623-5) argues against this assumption, and maintains that Medhâtithi's Nyâyashâstra need not necessarily refer to his Manubhâshya. In the Mahâbhârata (Shântiparvan 265.45 ed. Bangavâsi) we read that Medhâtithi is the very same person as Gautama (Keith 1923-25:625), so perhaps there is no need to assign the Pratimâ to a date beyond the tenth century A.D.
More recently, Couture examined the Bâlacarita act for act, systematically comparing this play with the Hindu sources Harivamsha and Bhâgavatapurâna, and the Jain Harivamsha (1992:113-144). He reaches the conclusion that the Bâlacarita is a Southern drama of the second half of the first millennium. The play is not based on the Bhâgavatapurâna, but on the Harivamsha recensions of the South, where the Jain versions were abundantly present (1992:144). This is more in line with the idea that Krshna plays are late (see Konow 1920:232, who for the rest considers the Bâlacarita as the only exception to this observation, as he is a supporter of the pro-Bhâsa theory).
Tieken (1993:36), finally, argues that the present Pratijnâ is not older than the Mattavilâsa (1993:36). He considers the Pratijnâ a patchwork, or rather a play with insertions and borrowings. A clear insertion would be the first scene of the third act, which is supposed to have been taken from the Mattavilâsa of Mahendravarman I (from 610 A.D. onwards) (1993:9-17), whereas elsewhere an influence would have come from Vishâkhadatta's Mudrârâkshasa (1993:18). Furthermore, even after deletion of the Mattavilâsa and the Mudrârâkshasa part, the remainder still is a pastiche, according to Tieken (1993:18). Already Zin-Oczkowska has pointed to the fact that the third act of the Pratijnâ might be a later addition (1990:180ff).
In addition, the characteristic beginning with sûtradhârakrtârambha would bear no relation at all to the opening found in the Trivandrum plays (1993:30). Bâna then refers to a Svapnavâsavadatta different from the one we know (1993:30-33).
Tieken distinguishes a group within the Trivandrum group. Five dramas - Abhisheka, Ûrubhanga, Pancarâtra, Pratimâ and Madhyama - are supposed to focus on the good result of the performance of a ritual (forthcoming, 1997). The main similarity is the appearance in the five plays of three persons who represent the three brahmins required at a ritual.