“Anthony Johnson, a free black, later owned the American Colonies’ first true slave”^
(Schneider, Carl and Schneider, Dorothy. Slavery in America, New York: Infobase Publishing, 2007) wikipedia
Long before Johnson owned a slave, the original "nigars" we repurchased and owned by someone (as far as I know we don't know whom), but we do know that in VA they did not have political rights, and in 1638 there was a slave auction in VA---to my knowledge no "indentured servant" auction ever occurred, because indentures were not regarded under English (borrowing from Roman) law defined as "movable property" as were VA slaves. So it is clear that at least in some (I would say, most) cases, "nigars" arrived with the presumption of servitude. Again, treatment gives clues as to STATUS, butt not PRACTICE. That is, any freeman at any time prior to the institutionalization of slavery in the mid1600s could free EITHER a slave or indenture. Some did, many did not.
iIn 1640, a slave was branded according to VA legal records. This did NOT occur with free men who had voluntarily signed indenture contracts. It is true that terms of indenture could be extended for a variety of reasons, sometimes effectively for life. But even then indentures were not viewed as disposable property. Indentures were NOT routinely chained, ESP. After arrival at destination. (Again, you can find exceptions for criminals placed into indenture in lieu of jail---but even these had time limits on their service.)
Someone bought and owned the 1619 "nigars" and someone bought "slaves" (all black) in 1638. Laws differed by colony---we have a black man apparently srvng in the MD legislature in 1640 or so.
In short, anyone thinking Johnson represented typical status of most blacks in the south prior to 1650 is making a serious mistake. There were actual blacks TREATED as indentures---but to my knowledge none ever signed a contract, nor were the signatures (or witness testimony) of black indentures ever recognized (whites were), but the majority were not freed or the numbers of free men of color would have exploded between 1620 and 1660, but instead salve numbers grew.