MPEC 2012-J26 1999 OQ3 (2012 Apr positions linked to 1999 Jul-Oct positions)
MPEC 2012-J27 2012 FB57 = 2008 VO12 (2012 Mar-Apr positions linked to 2008 Nov positions)
MPEC 2012-J28 2010 VZ71 = 2010 MB113 (2010 Nov-2011 Jan positions linked to 2010 Jun positions)
MPEC 2012-J29 2009 EV = 2008 PG1 (2009 Mar positions linked to 2008 Aug positions)
2008 PG1 was only observed on two nights in August 2008, discovered by LINEAR on August 3 and observed 16 hours later from Great Shefford on the morning of Aug 4th, the discovery was announced the same day in MPEC 2008-P14. Attempts were made from Great Shefford to recover it on the next two clear nights but without success and it was the subject of a note here in September 2008. With a very uncertain orbit it was listed by JPL as a Virtual Impactor with the first (very low probability) impact with Earth predicted to happen as early as 2013.
Update 15 May 2012: Following the linkage and subsequent orbital improvement, the JPL Sentry system has been able to remove 2009 = 2008 PG1 from their list of potential future Earth impact events.
Following the linkage of 2009 EV to 2008 PG1 by the MPC, the images taken at Great Shefford on the mornings of 2008 Aug. 9th and 13th were re-examined to check whether 2008 PG1 would have been in the field of view during those search attempts. On Aug. 9th, four fields were taken, spanning 1° but further searching had to be abandoned because of the approaching dawn. Unfortunately, just one more field would have picked it up, close but not close enough. With a rapidly expanding uncertainty area, fields taken on the morning of Aug 13th were all more than 2.5° away from the actual position.