With Yeri's recent addition to girl group Red Velvet and no word of explanation from SM Entertainment, netizens have been abuzz with questions. Why a new member? Why didn't she debut with Red Velvet from the start? Some are even wondering: are there more members to come? 

Recently, a netizen posted on online community Instiz the theory that Red Velvet may be a rotational group and that the member lineup might change at any time. 

In the post titled "Red Velvet rotation group," the netizen muses that SM seemed to have hinted at Yeri's addition by including her in Red Velvet's debut MV "Happiness" along with six other female SM trainees. The netizen uploads the following picture, a collage of screenshots from the MV. Yeri is the girl wearing red shown on the bottom left in the second picture. 

The netizen adds that a few months ago, these same rookies, including Yeri, were strangely introduced to the public on stage for an SM concert, likely the 'SMTOWN Live World Tour IV.' Only female trainee Rami was missing. 

Perhaps this is the lineup that could join Red Velvet at anytime? 

The netizen further points out that even after Red Velvet's debut, the girls Seulgi, Irene,Wendy, and Joy are still listed under trainee group S.M.ROOKIES as if they are still trainees rather than official members. The netizen concludes, "It seems highly likely that Red Velvet is a rotational group." 

Netizens seem convinced by the post's evidence and have mostly reacted negatively to the possibility. Comments include, "SM Entertainment, what's wrong with you, don't be like that TT," "Ah, really TT," "Please I'm begging you TT," "SM is letting us down...," and, "In the video for the Shanghai SM concert, [Red Velvet] came out with the rookies, too... TT." 

The last comment refers to the Shanghai 'SM Town' concert clip below. When S.M.ROOKIES are introduced at the 1:20 mark, an image of Red Velvet leading the trainees can be seen. 

Considering After School and Nine Muses' graduation concept, I wouldn't be surprised if a rotational concept was thrown into the K-Pop mix. The question is if fans would be accepting of it.

Another rumor is that Red Velvet might be a sub-unit in a larger group, which would be another interesting twist.  What do you guys think? Do the rumors seem pretty valid so far or are netizens freaking out over nothing?