I receiveid Hoya sp.  aff  erythrostemma IML 1423 as a cutting from a friend in Florida in the summer of 2011, and it finally flowered in the late autumn of 2014.  It hales from Thailand and has a flower that is very similar to Hoya mindorensis.  I do however find it much easier to cultivate than H. mindorensis.  The flowers are very long lived, lasting a full two weeks; it is also a heavy nectar dripper so mind the mess on this one.  I have always grown this one in potting mix and have given it no special care.  It may have flowered for me after putting it directly outside for the summer and then moving it into a well lit humid grow tent in the fall.