about hg19 reference gene coordinate file

[xuexingwangzhedishitian]

I downloaded hg19 reference gene coordinate file by R code from you. this reference gene coordinate file has three types of gene name including Ensembl ID, Entrez ID and gene symbol, then, used gene symbol for gene mapping for CNV. I noticed that the column 'gene symbol' has duplicated genes.
so, I repeated this code below.
TCGAbiolinks:::get.GRCh.bioMart(genome = "hg19")
I found three types of gene name have duplicated genes or missed genes.
I want to ask that how work this situation. It must affect downstream analysis.