C86 tape (the object) of the C86 Spirit (the genre).
My Bloody Valentine (MBV) existed long before Bilinda Butcher, but sounded like a completely different band (closer to post-punk gothic and garage rock).
May 1986 release of the C86 tape by NME. MBV was not on the original tape.
September 1986 MBV releases The New Record, which is their album that most closely resembles the "C86" sound (noisy and melodic pop), still with the original vocalist, Dave Conway.
April 1987 Dave Conway leaves the band and Bilinda Butcher joins.
When Bilinda joined the group, the "C86 phenomenon" was at its peak/end, and the band was about to evolve into what would become Shoegaze.
MBV and the C86 Scene Although My Bloody Valentine wasn't on the original NME tape, they are often associated with the "C86 generation." They played on the same circuits as bands like The Pastels or Primal Scream. Their sound in 1986 was the so-called "Anorak Pop" (jangle guitars and sweet melodies), which defined the C86 aesthetic.
Bilinda's arrival in 1987 was the catalyst that took the band away from the C86 aesthetic.
With her, the vocals became more ethereal, "whispered," and integrated into the mass of sound, moving away from the youthful pop of the NME tape and towards the absolute distortion of Isn't Anything (1988) and Loveless (1991). C86 (1986): Peak of naive Jangle Pop / Indie. MBV (without Bilinda) attempts this sound.
Post-C86 (1987 onwards): Bilinda Butcher enters, the sound becomes denser, more sensual and noisy. Shoegaze is born.
Basically, Bilinda is the figure that marks the transition from classic Indie Pop (C86) to modern Shoegaze.