Implantation Bleeding

Is it possible for implantation bleeding to be late? My friend took a test in Dec and it was neg then she bleed in Jan and I think it was normal bleeding then she took a test in Feb and it was positive.... She is pg... I took a test May 2nd and it was neg then I took another one 2 weeks later and it was positive so I got a blood test done it was neg... I bleed for 2 days in May around the 7th and 8th then I bleed for 4 days in June.... Could my implantation bleeding be late like my friends was....